# Mode in a stream of integers (running integers)

Given that integers are being read from a data stream. Find the mode of all the elements read so far starting from the first integer till the last integer.

Mode is defined as the element which occurs the maximum time. If two or more elements have the same maximum frequency, then take the one with the last occurrence.

Examples:

Input: stream[] = {2, 7, 3, 2, 5}
Output: 2 7 3 2 2
Explanation:
Mode of Running Stream is computed as follows:
Mode({2}) = 2
Mode({2, 7}) = 7
Mode({2, 7, 3}) = 3
Mode({2, 7, 3, 2}) = 2
Mode({2, 7, 3, 2, 2}) = 2

Input: stream[] = {3, 5, 9, 9, 2, 3, 3, 4}
Output: 3 5 9 9 9 3 3 3

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach: The idea is to use a Hash-map to map elements to its frequency. While reading the elements one by one update the frequencies of elements in the map and also update the mode which will be the mode of the stream of the running integers.

Below is the implementation of the above approach:

## C++

 `// C++ program to implement ` `// the above approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function that prints ` `// the Mode values ` `void` `findMode(``int` `a[], ``int` `n) ` `{ ` `     `  `    ``// Map used to mp integers ` `    ``// to its frequency ` `    ``map<``int``, ``int``> mp;  ` ` `  `    ``// To store the maximum frequency ` `    ``int` `max = 0; ` ` `  `    ``// To store the element with ` `    ``// the maximum frequency ` `    ``int` `mode = 0; ` `     `  `    ``// Loop used to read the ` `    ``// elements one by one ` `    ``for``(``int` `i = 0; i < n; i++)  ` `    ``{ ` `         `  `        ``// Updates the frequency of ` `        ``// that element ` `        ``mp[a[i]]++; ` `     `  `        ``// Checks for maximum Number ` `        ``// of occurrence ` `        ``if` `(mp[a[i]] >= max)  ` `        ``{ ` `     `  `            ``// Updates the maximum frequency ` `            ``max = mp[a[i]]; ` `     `  `            ``// Updates the Mode ` `            ``mode = a[i]; ` `        ``} ` `        ``cout << mode << ``" "``; ` `    ``} ` `} ` `     `  `// Driver Code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 2, 7, 3, 2, 5 }; ` `    ``int` `n = ``sizeof``(arr)/``sizeof``(arr); ` ` `  `    ``// Function call ` `    ``findMode(arr, n); ` ` `  `    ``return` `0; ` `}  ` ` `  `// This code is contributed by rutvik_56 `

## Java

 `// Java implementation of the ` `// above approach ` ` `  `import` `java.util.*; ` ` `  `public` `class` `GFG { ` ` `  `    ``// Function that prints ` `    ``// the Mode values ` `    ``public` `static` `void` `findMode(``int``[] a, ``int` `n) ` `    ``{ ` `        ``// Map used to map integers ` `        ``// to its frequency ` `        ``Map map ` `            ``= ``new` `HashMap<>(); ` ` `  `        ``// To store the maximum frequency ` `        ``int` `max = ``0``; ` ` `  `        ``// To store the element with ` `        ``// the maximum frequency ` `        ``int` `mode = ``0``; ` ` `  `        ``// Loop used to read the ` `        ``// elements one by one ` `        ``for` `(``int` `i = ``0``; i < n; i++) { ` ` `  `            ``// Updates the frequency of ` `            ``// that element ` `            ``map.put(a[i], ` `                    ``map.getOrDefault(a[i], ``0``) + ``1``); ` ` `  `            ``// Checks for maximum Number ` `            ``// of occurrence ` `            ``if` `(map.get(a[i]) >= max) { ` ` `  `                ``// Updates the maximum frequency ` `                ``max = map.get(a[i]); ` ` `  `                ``// Updates the Mode ` `                ``mode = a[i]; ` `            ``} ` ` `  `            ``System.out.print(mode); ` `            ``System.out.print(``" "``); ` `        ``} ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `main(String[] args) ` `    ``{ ` `        ``int` `arr[] = { ``2``, ``7``, ``3``, ``2``, ``5` `}; ` ` `  `        ``int` `n = arr.length; ` ` `  `        ``// Function Call ` `        ``findMode(arr, n); ` `    ``} ` `} `

## Python3

 `# Python3 implementation of the  ` `# above approach ` ` `  `# Function that prints  ` `# the Mode values  ` `def` `findMode(a, n): ` `     `  `    ``# Map used to mp integers  ` `    ``# to its frequency  ` `    ``mp ``=` `{} ` `     `  `    ``# To store the maximum frequency  ` `    ``max` `=` `0` `     `  `    ``# To store the element with  ` `    ``# the maximum frequency  ` `    ``mode ``=` `0` `     `  `    ``# Loop used to read the  ` `    ``# elements one by one  ` `    ``for` `i ``in` `range``(n): ` `        ``if` `a[i] ``in` `mp: ` `            ``mp[a[i]] ``+``=` `1` `        ``else``: ` `            ``mp[a[i]] ``=` `1` `         `  `        ``# Checks for maximum Number  ` `        ``# of occurrence      ` `        ``if` `(mp[a[i]] >``=` `max``): ` `             `  `            ``# Updates the maximum  ` `            ``# frequency  ` `            ``max` `=` `mp[a[i]] ` `             `  `            ``# Updates the Mode  ` `            ``mode ``=` `a[i] ` `             `  `        ``print``(mode, end ``=` `" "``) ` ` `  `# Driver Code ` `arr ``=` `[ ``2``, ``7``, ``3``, ``2``, ``5` `] ` `n ``=` `len``(arr) ` ` `  `# Function call  ` `findMode(arr,n) ` ` `  `# This code is contributed by divyeshrabadiya07 `

## C#

 `// C# implementation of the ` `// above approach ` `using` `System; ` `using` `System.Collections.Generic; ` `class` `GFG{ ` ` `  `    ``// Function that prints ` `    ``// the Mode values ` `    ``public` `static` `void` `findMode(``int``[] a, ``int` `n) ` `    ``{ ` `        ``// Map used to map integers ` `        ``// to its frequency ` `        ``Dictionary<``int``, ``int``> map = ``new` `Dictionary<``int``, ``int``>(); ` ` `  `        ``// To store the maximum frequency ` `        ``int` `max = 0; ` ` `  `        ``// To store the element with ` `        ``// the maximum frequency ` `        ``int` `mode = 0; ` ` `  `        ``// Loop used to read the ` `        ``// elements one by one ` `        ``for` `(``int` `i = 0; i < n; i++)  ` `        ``{ ` `         `  `            ``// Updates the frequency of ` `            ``// that element ` `            ``if` `(map.ContainsKey(a[i]))  ` `            ``{ ` `                ``map[a[i]] = map[a[i]] + 1; ` `            ``} ` `            ``else` `            ``{ ` `                ``map.Add(a[i], 1); ` `            ``} ` ` `  `            ``// Checks for maximum Number ` `            ``// of occurrence ` `            ``if` `(map[a[i]] >= max)  ` `            ``{ ` ` `  `                ``// Updates the maximum frequency ` `                ``max = map[a[i]]; ` ` `  `                ``// Updates the Mode ` `                ``mode = a[i]; ` `            ``} ` `            ``Console.Write(mode); ` `            ``Console.Write(``" "``); ` `        ``} ` `    ``} ` ` `  `    ``// Driver Code ` `    ``public` `static` `void` `Main(String[] args) ` `    ``{ ` `        ``int``[] arr = {2, 7, 3, 2, 5}; ` `        ``int` `n = arr.Length; ` ` `  `        ``// Function Call ` `        ``findMode(arr, n); ` `    ``} ` `} ` ` `  `// This code is contributed by Amit Katiyar `

Output:

```2 7 3 2 2
```

Performance Analysis:

• Time Complexity: O(N)
• Auxiliary Space: O(N)

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